Note how camera and smartphone advertisements talk mainly about Megapixels, and they have been using this for years as a marketing trick as if having more Megapixels were the only thing that matters about camera quality. The truth is quite different.
How a digital camera works
In order to understand that Megapixels are not the only thing that matters in a camera, first let us see, in a simplified way, how a digital camera works.
Light rays reach the lenses and they are directed to the sensor. The sensor converts the light into electrical signals, which are digitalized assigning a colour to every pixel. Finally, the photo is saved onto the memory card.
The sensor surface has to be divided into very small areas, one for every pixel. Therefore, for a certain sensor size, the more Megapixels a camera has, the smaller the area that can be assigned to every pixel.
The better the lenses, the higher their precision to direct the light rays to every part of the sensor, and the more precise the sensor, the less contaminated every pixel will be by light corresponding to adjacent pixels.
More Megapixels does not mean more quality
The quality of a camera is decisively influenced by the sensor quality, not only by its Megapixel resolution. In addition to this, the quality of the lenses that you use play an essential role, and even more when you handle more Megapixels. So you may find a camera or smartphone which, having less Megapixels, but with a better sensor and better lenses, gets clearer images than other cameras with more Megapixels.
Take into account that the more pixels, the smaller the area size in the sensor to catch the light (the colour) corresponding to every pixel and, therefore, the higher the precision must be in both the sensor and the lenses. So much so that there have been cases with camera models from well known brands whose Megapixel resolutions were reduced when the next models were released.
Basically, if you use a worse camera and worse lenses with more Megapixels, you will have more worse quality pixels. Or what is the same, if you already have a good camera or smartphone, do not worry if a new model has just been released, your photos are not going to have much less quality.
If you use a worse camera and worse lenses with more Megapixels, you will have more worse quality pixels.
Think about this: with a 16 Mpx camera you can already print photos with high quality (that is, 300 dots per inch) with a size up to 39 cm x 29 cm (15.4 inches x 11.4 inches). A 20 Mpx camera have 4 Mpx more, which means 25 % more, but these additional pixels are spread along the width and the height, so with 300 dpi you could print up to 43 cm x 32 cm (17.2 inches x 12.9 inches). The difference is not as big as you thought, ¿right?
Besides, if your camera and your lenses, with 16 Mpx, are better than the 20 Mpx camera that your friend has just bought, you will have better results printing your larger photos than him.
And if we are talking about large format prints, for example pictures for hanging on the wall, keep in mind that the viewing distance comes into play. Basically, the larger the photo, the farther away you will be to look at it and your eyes will not be able to distinguish individual dots on the paper. Therefore, you will need a lower dpi resolution (dots per inch).
In conclusion, do not choose a camera or smartphone just for its Megapixel resolution. Choose for the sensor quality, the lenses quality, the ability to take photos under lower light conditions, etc. And if it also has more Megapixels, even better.
Advantages of having more Megapixels
At this point, it will be a little clerarer that more Megapixels does not mean more quality. But, having the same photo quality, does having more Megapixels offer any additional advantage? One of the practical advantages is that sometimes you will want to use only a part of an image. In this situation, even if you crop the picture and you only take a smaller part of it, you will continue having enough number of pixels to print with a large size.
But remember, as we told you above, that more megapixels does not mean more quality. The crisper the original photo (good light, properly focused, etc.), the better the results that you will get even having less pixels.
How big can I print my photos?
If you want to understand better concepts like pixel resolution, dpi resolution and print sizes, we recommend our article How big can I print my photos?, where we also provide you with an interactive tool so you will not need a calculator.
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